Editable Gridview to edit underlying DataTable in ASP.NET (C#)

In my ASP.NET code in C# (VS 2008) I have created a gridView and here is the .aspx code:

        <asp:GridView ID="grid1" runat="server">
        </asp:GridView>

In aspx.cs code I have created a DataTable via program code and I could bind to the GridView by this code:

            grid1.DataSource = dsOut;
            grid1.DataBind();

dsOut above has variable number of columns and unknown column names (names of the columns are determined in the program code).
The content shows in the GridView correctly. How can I make the GridView  editable so that after the Submit button is pressed --

 protected void btn1_Click(object sender, EventArgs e)
    {
        DataTable dt = (DataTable)grid1.DataSource;
    }

The above works. I can get the data in "dt" but all I need it seems to make the GridView editable..
thanks.